1. Field of the Invention
This invention pertains to wire tensioning apparatus and more particularly to apparatus for twisting multiple strand wires to produce longitudinal tension therein.
2. Description of the Prior Art
A conventional method of securing heavy loads to trucks and other vehicles is to tension chains, straps, or other hold-down devices. A preferred hold-down arrangement includes a metal wire composed of several strands that are twisted about each other to produce the desired longitudinal tension in the wire. The twisted wire technique has not been utilized to the maximum extent because of a lack of suitable wire twisting devices. U.S. Pat. No. 549,494 shows a simple hand twisting tool. Although the tool of the U.S. Pat. No. 549,494 possesses the advantage of light weight and portability, it is evident that the tool is limited to twisting relatively light wires, and that the amount of wire longitudinal tension is limited by the strength of the workmen using it. U.S. Pat. No. 3,590,391 discloses a three-handled hand twister that opens and closes to engage and disengage the wire. The manipulation of the twisting device of the U.S. Pat. No. 3,590,391 is cumbersome. The device is further handicapped because the wire tension obtainable is dependent on the strength of the workmen. U.S. Pat. No. 3,169,559 illustrates a portable power operated tool that ties the ends of U-shaped wires by twisting. It is evident that the tension produced in a tied wire is minimal and that the tool of the U.S. Pat. No. 3,169,559 is not suitable for securing heavy loads to vehicles.
U.S. Pat. No. 1,488,980 teaches a non-portable wire working machine that may be either hand or power operated. The machine operates on a fixed cycle that limits the amount of twist imparted to the wire strands. Increased twisting is possible by rotating the twisting mechanisms through increased angles during each cycle. However, the increased angle of twist necessarily limits the amount of torque available for twisting. Further, the amount of twist is fixed for each cycle, and thus wire tension cannot be controlled to suit the application at hand. The use of the wire twisting pin as a drive member further limits the torque transmitting capacity. It is apparent that the machine of U.S. Pat. No. 1,488,980 is suitable only for light wires, and for applications wherein an uncontrolled amount of twist is satisfactory.
Thus, a need exists for heavy duty but portable apparatus that is capable of twisting wire strands with controlled force sufficient to secure heavy objects to desired locations.